Question 41847
R(d) = 25/d^2 means that the resistance is a function of the diameter.  To see how the size of the diameter effects resistance, plug in numbers for the diatmeter (d) and see what happens to the value of resistance (R):

Let d = 1:
R(1) = 25/1^1 = 25
.
Let d = 2
R(2) = 25/2^2 = 6.25
.
Let d = 5
R(5) = 25/5^2= 1
.
Let d = 10
R(10) = 25/10^2 =  .25

So it seems that as the diameter (d) increases, the value of the resistance (R) decreases.  This represents an inverse relationship between (d) and (R).  Therefore, when (d) decreases, (R) increases.  Try to plot these values to better visualize this inverse relationship between diameter and resistance.